This invention generally relates to rotary tool assemblies of the type including a tool holder, a cutting tool retainer, and a lockring, and is specifically concerned with an apparatus and method for balancing such a rotary tool assembly by means of a pair of balancing rings rotatably mounted around the circumference of the lockring.
Mechanisms for balancing rotary tool holder assemblies are known in the prior art. Many of such tool holder assemblies are capable of operating at speeds above 12,000 rpm. Without a balancing mechanism, the smooth and accurate operation of the cutting tool held by such a rotary tool assembly would be greatly impaired, as the centrifugal forces created within an unbalanced, high speed tool holder can cause the cutting tool to vibrate, which in turn results in an uneven cutting action as well as stresses in the tool which can result in premature wear or even failure.
The operation of such prior art balancing mechanisms usually involves the two steps of measuring the amount of unbalance in the rotary tool assembly after a cutting tool has been mounted therein, and then moving the position of a mass in the balancing mechanism to neutralize the unbalance in the tool holder. Unfortunately, there are a number of shortcomings associated with all such prior art designs. For example, in one prior art balancing mechanism, three or more radially oriented screws are screwed either inwardly or outwardly with respect to the axis of rotation of the tool holder in order to achieve balance. While this mechanism is generally capable of achieving its intended function, its operation is often tedious and difficult as the various screws making up the mechanism have to be precision turned different amounts. This mechanism is also limited in the amount of unbalance it can correct without the addition of more screws which would make the adjustment operation even more complicated and tedious. In another type of mechanism, cooperating open-type rings are rotated about the axis of a rotating tool holder in order to achieve a tool balance. Such a mechanism is disclosed and claimed in U.S. Pat. No. 4,626,144. However, the balancing rings used in this mechanism are mechanically linked together and cannot be moved or adjusted independently, thereby limiting the versatility of the mechanism. Additionally, this particular prior art balancing mechanism is relatively complicated and hence expensive to manufacture.
One of the most recent and substantial advances in the balancing mechanism art comprises a pair of independently rotatable balancing rings mounted on bearing surfaces that circumscribe the cylindrical exterior of the tool holder of a rotary tool assembly. This balancing mechanism is disclosed and claimed in U.S. Pat. No. 5,074,723, assigned to Kennametal Inc. However, the applicants have observed a number of areas in which even this mechanism might be improved. For example, in order for the tool holder of the tool assembly to accommodate the balancing rings, the body of the tool holder must be made longer along its axis of rotation, and further must include not only a pair of circumscribing bearing surfaces for rotatably mounting the bearing rings, but a retaining ring as well for securing the balancing rings to the housing of the tool holder. Thus the tool holder component of the tool assembly must be custom made to accommodate the balancing mechanism. The necessity of providing a specially dimensioned and machined tool holder to accommodate the balancing mechanism causes the resulting, balanceable rotary tool assembly to be more expensive than it would be if the balancing mechanism could be installed in an existing tool assembly without the need for replacing the tool holder or any of the other components of the assembly.
Clearly, there is a need for an improved balancing-ring type mechanism that can be installed in a rotary tool assembly without the need for a specially made tool holder. Ideally, such a balancing ring mechanism could be quickly and inexpensively installed on an existing conventional rotary tool assembly without the need for specially manufacturing any of the major components of the assembly, and with only a minimum amount of machining on existing, conventional parts of the assembly.